1. Field of the Invention
The present invention relates to an optical-fiber-spliced portion reinforcing heating device.
2. Description of the Related Art
Generally, when optical fibers are fusion-spliced, the following work sequence is carried out.
(1) An optical fiber is extracted from an optical fiber cable.
(2) A resin coating (front end) that coats the extracted optical fiber is removed by a removing tool of an optical fiber coating.
(3) After the coating is removed from the front end, scraps of the resin coating remain on a surface of a glass (bare optical fiber) of the optical fiber, and the scraps are removed by a cloth or a paper moistened with alcohol.
(4) The clean optical fiber is cut by an optical fiber cutter.
(5) The cut optical fibers are fusion-spliced by an optical fiber fusion splicer.
(6) The post-fusion-spliced optical fiber is covered with a heat-shrinkable reinforcement sleeve and is heat-reinforced by a heater of a fusion splicer.
(7) The heat-reinforced optical fiber is accommodated in a storage tray of a spliced portion storage case.
In the above-described step (6), the outer side of the sleeve used to reinforce the optical fiber spliced portion is formed of a heat shrinkable tube, a hot melt disposed inside thereof is molded at the circumference of the optical fiber, and the spliced portion is thereby protected.
The sleeve formed by the outer heat shrinkable tube and the inner hot melt is heat-shrinkable depending on various coating diameters of the optical fiber.
Additionally, as a result of heat-shrinking the sleeve at substantially the center in the longitudinal direction thereof at first, the sleeve is molded while extruding air inside the sleeve from the sleeve center to the outside thereof.
The optical fiber spliced portion that is reinforced by the above-described sleeve also has a function of blocking an external substance such as moisture which adversely affects an optical fiber.
Between the outer heat shrinkable tube and the inner hot melt, a stainless-steel tensile strength member is inserted into the sleeve in advance in the case of a single-core optical fiber and a glass tensile strength member is inserted into the sleeve in advance in the case of a multi-core ribbon, and a structure that resists bending or tension is thereby realized.
Moreover, shrinking can be carried out at high speed such as approximately 30 seconds by use of an optical-fiber-spliced portion reinforcing heating device which is conventionally mounted on an optical fiber fusion splicer.
In order to heat-shrink a sleeve, in recent years, polyimide film heaters are used which are adhesively attached to a metal sheet and serve as a heater provided on an optical-fiber-spliced portion reinforcing heating device (hereinbelow, may be referred to as a reinforcing heating device); and a heater is proposed as an example having single flat sheet heater into which two or more heaters circuit patterns are implanted (for example, refer to Japanese Patent No. 3293594, hereinafter referred to as Patent Document 1 and refer to Japanese Unexamined Patent Application, First Publication No. 2010-249887, hereinafter referred to as Patent Document 2).
As mentioned above, generally, a plurality of heater circuit patterns are implanted into a flat sheet heater.
Furthermore, a technique of working and heating a flat sheet heater in a U-shape is also proposed (for example, refer to Japanese Patent No. 4165375, hereinafter referred to as Patent Document 3).
Furthermore, generally, in order to prevent a sleeve from being positionally displaced from an optical fiber spliced portion when tension is applied to an optical fiber from the outside before heat shrinking of the sleeve, a clamp is provided at a reinforcing heating device.
As such clamp, a clamp provided with a tension applying mechanism is known, and by using this, an optical fiber is prevented from going slack in the sleeve.
If the sleeve shrinks in a state in which the optical fiber has a slack, stress remains in the optical fiber inside the sleeve, there is a concern that the long-term reliability of the optical fiber is degraded; particularly, in the reinforcing heating device that reinforces a ribbon by heating, the clamp is an essential and necessary configuration to prevent arrayed bare optical fibers from coming in contact with each other.
If tension is not applied to the fiber, the optical fibers adjacent to each other shrink in a state of being in contact with each other, damaging both optical fibers, and therefore, the long-term reliability of the optical fiber is decreased.
In order to solve the aforementioned problems, a reinforcing heating device used for multi-core tape fibers is proposed, in which clamps are arranged at both sides of the heater in the longitudinal direction of the optical fiber, one of the clamps is configured to slidably move in the longitudinal direction of the optical fiber, and a compression coil spring is provided (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2000-321462, hereinafter referred to as Patent Document 4).
In a constitution of Patent Document 4, a tension is applied to an optical fiber by use of a clamp in the sequence described below.
In a first method, an optical fiber is set in a state in which right and left clamps are opened, the movable left clamp is only closed, subsequently, the optical fiber is pulled in the right direction, and the right clamp is closed in a state in which a compression coil spring is contracted.
At this time, the shrinkage of the compression coil spring is designed to generate optimal tension in the optical fiber at the position at which the movable left clamp is brought into contact with the right end of the movable range, and the optimal tension of the compression coil spring is always applied to the optical fiber.
Additionally, in a second method, the left side face of a movable clamp is pressed in the right direction with the finger in a state in which right and left clamps are opened, shrinkage of a compression coil spring is designed to cause an optical fiber to generate an optimal tension at the position with which the left clamp is brought into contact in the right direction.
Thereafter, the optical fiber is set to the clamp in a state of being pressed with the finger, the movable left clamp and the fixed right clamp are closed.
Subsequently, by removing the finger from the movable left clamp, an optimal tension due to the compression coil spring is always applied to the optical fiber.
However, the method disclosed in the above-mentioned Patent Document 4, in a state after the optical fiber is set to the clamp without slack by pulling it with the finger and the right and left clamps are closed, a forward movable range that allows the movable left clamp to further move toward the heater side does not remain almost, and a backward movable range is only ensured in this state.
In above-described state, in the case of applying an excessive lateral pressure to the optical fiber, there is a problem in that a residual tensile force that causes the long-term reliability of the optical fiber to be significantly deteriorated is applied to the optical fiber or the optical fiber is immediately broken.
Furthermore, instead of the aforementioned compression coil spring, application of a tension to an optical fiber by utilizing a magnetic force is proposed (refer to, for example, Japanese Patent No. 3337874, hereinafter referred to as Patent Document 5).
In FIG. 1 or the like shown in Patent Document 5, a right clamp is movable and a left clamp is fixed.
The movable clamp is generally pressed onto a heater side by a tension coil spring.
Subsequently, when the optical fiber is grasped (clamped) and the lid of the heater is closed, a repulsion force is generated between magnets, and a tension is applied to the optical fiber.
Because of this, complicated steps such as two methods disclosed in Patent Document 4 are not necessary, and the tension is automatically applied to the optical fiber by only closing the clamp or the lid.
However, in the technique disclosed in Patent Document 5, similarly, the optical fiber is set to the clamp without slack by pulling it with the finger, a movable range that allows the movable clamp to further move toward the heater side hardly remains in a state after the right and left clamps are closed, and a backward movable range is only ensured in this state.
In above-described state, in the case of applying an excessive lateral pressure to the optical fiber, there is a problem in that a residual tensile force that causes the long-term reliability of the optical fiber to be significantly deteriorated is applied to the optical fiber or the optical fiber is immediately broken.
In addition, generally, for a reinforcing heating device used for a single-core optical fiber, a device that is provided with a mechanism applying tension does not almost exist.
The reason is that, adjacent optical fibers are in contact with each other in the case of a single-core optical fiber, and therefore, in most cases, in order to reduce the cost of the device, it is not provided therefor.
That is, such mechanism applying tension to an optical fiber is mainly mounted on a reinforcing heating device used for a multi-core optical fiber.
Here, in the case of shrinking the sleeve in a state in which a tension is applied to the optical fiber, a residual tension remains in the optical fiber.
In the case of a normally-used optical fiber having the surface which is not damaged, a long-term reliability is not degraded under a residual tension of 100 gf or less. Conventionally, it is recommended for the residual tension of an optical fiber to be less than or equal to 100 gf (for example, refer to Japanese Unexamined Patent Application, First Publication No. H10-332979, hereinafter referred to as Patent Document 6).
However, a fusion-spliced optical fiber may be damaged due to the work operation therefor. Therefore, in the case where, for example, a tension is 200 gf under a rupture evaluation test after the optical fibers are spliced, it is recommended to be less than or equal to 30 gf.
Generally, in the case of splicing optical fibers, the amount of time of fusion-splicing is less than or equal to 10 seconds; however, an amount of time of 25 seconds or more is required for heat shrinking.
For example, it is believe to take 40 seconds to connect an optical fiber to a reinforcing heating device or to remove the optical fiber therefrom.
Generally, dozens of optical fibers are provided in one optical fiber cable, so, it takes approximately 1 hour to splice together ninety-six optical fibers (96 fibers×40 seconds=3840 seconds≈1 hour). Thus, it takes 1 hour only to carry out an operation of heat-reinforcing sleeve in order to splice one cable, and shortening of heat shrinking time is important.
Generally, in a device which heat-reinforce an optical fiber spliced portion, as a result of pressing a sleeve onto a heater and thereby deforming the sleeve, it is possible to shorten the heating time by heating the sleeve in a state in which the area of contact between the heater and the sleeve increases and the heat is easily transmitted.
Hitherto, a plurality of techniques of shortening the heating time as a result of positively causing the heater to come into contact with the sleeve are proposed.
Here, in the aforementioned Patent Document 6, a method of pressing a heater onto a sleeve by use of a compression coil spring and of always maintaining the contact state is described.
In Patent Document 6, a mechanism is provided which absorbs a tension by use of a compression coil spring when the tension is applied to an optical fiber by pressing by a heater.
Moreover, in this constitution, as a result of providing the left slide clamp and the compression coil spring, a tension is applied to an optical fiber so as to prevent occurrence of a slack thereof in a manner similar to a conventional heating device.
However, in the left slide clamp of Patent Document 6, the backward movable range explained above is ensured; however, a forward movable range is not provided.
In the case where an allowable residual tension of an optical fiber is 10 to 100 gf, the total pressing force due to a heater is required to be less than or equal to 10 to 100 gf.
In the case where, for example, a tension is 200 gf under a rupture evaluation test after the optical fibers are spliced, the allowable tension is less than or equal to approximately 30 gf, and the pressing force due to a heater is required to be less than or equal to 30 gf.
As will be described later, there is a problem in that the sleeve cannot be sufficiently deformed in 30 gf.
Even it a pressing force of several hundreds of gf is applied to the heater at the side surface thereof, a compression coil spring that applies a tension of 30 gf thereto is unconscionably and quickly shrunk, a forcible tension of several hundreds of gf is applied to the optical fiber, and there is a problem in that the long-term reliability of the optical fiber after reinforcement is degraded.
As a result, in Patent Document 6, it is not possible to increase the pressing force of the heater to be greater than the allowable residual tension of the optical fiber.
Here, a method of always maintaining the contact between the heater and the sleeve by causing a hard core provided in the sleeve to be in close contact with a magnet is proposed (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2010-217271, hereinafter referred to as Patent Document 7).
However, in the method of Patent Document 7, the hard core inside the sleeve and the heater are attracted to each other due to the magnet; however, there is a problem in that, in the sleeve structure, a pressing force to deform the entire sleeve by squashing cannot be applied thereto.
For this reason, the contact between the heater and the sleeve can be maintained; however, the effect of increasing the contact area thereof can hardly be obtained.
Furthermore, in the case where the hard core is made of glass, it does not function.
Additionally, in the case of using a permanent magnet, since the magnet is disposed near the heater, there is a problem of degradation in magnetic force which is due to a high temperature.
In other case, a constitution is proposed which serves as a device of heat-reinforcing an optical fiber spliced portion, includes: a means of driving a heater by use of using a motor or the like; and a means of detecting that the heater moves forward to a predetermined position, i.e., a position where the sleeve is shrunk, and is configured to retreat after the heater moves forward to the sleeve position and the heater reaches a predetermined position (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2004-042317, hereinafter referred to as Patent Document 8).
According to Patent Document 8, two heaters press the sleeve, the area of contact between the sleeve and the heater increases, and it is possible to speed up the heat shrinking of the sleeve.
Particularly, the heat conduction efficiency due to the heater becomes higher, it is possible to shorten the heat shrinking time of the sleeve.
According to this system, it is possible to sufficiently deform the sleeve.
The inventor intensively researched how degree of the pressing force is applied to the sleeve so as to be deformed in order to shorten the heat shrinking time to be shortest; it is apparent that the pressing force of 500 gf to press the sleeve by the heater is required when the sleeve is heat-shrunk.
As shown in the chart of FIG. 30, as the pressing force of the sleeve becomes higher, the contact area between the heater and the sleeve increases, and the shrinking time of the sleeve becomes short.
FIG. 30 is a chart showing a case where a commonly-used sleeve of 60 mm which is used for single core is sandwiched between two heaters and heating is carried out at a temperature of 230° C. of both two heaters where one of the heaters is fixed and the other of the heaters is movable.
It is understood from this chart that, when the pressing force exceeds 500 gf, the pressing effect decreases, the shrinking time of the sleeve is not much shorter.
In addition, the aforementioned changing point of approximately 500 gf varies with the sleeve structure. Particularly, in the case of a commonly-used sleeve of 60 mm which is used for single core, the variation in the shrinking time reduces when the pressing force exceeds approximately 500 gf.
However, in the technique disclosed in Patent Document 8, there is problems described below.
Firstly, there is a first problem due to pressure of the sleeve by movement control of a heater.
The heater moves forward by a motor through a micrometer, it is necessary for the amount of the forward movement and the forward velocity thereof to control depending on a state in which a sleeve is contracted.
However, various kinds of sleeve are used, the amount of forward movement and the forward velocity vary depending on, for example, difference in the diameter or the material thereof.
Furthermore, a contractile rate of the sleeve varies depending on an outdoor temperature or a voltage of a built-in battery.
In addition, in the longitudinal direction of the sleeve, generally, the contractile rate of the center portion thereof is different from that of the outer-edge portion thereof.
Consequently, in the case where the heater excessively moves forward, an excessive pressure reaches the optical fiber provided thereinside, and the optical fiber is thereby damaged.
Alternatively, if the forward movement of the heater is delayed, a gap occurs between the heater and the sleeve, there is also a problem in that the sleeve is not shrunk in a shorter amount of time.
In order to make the pressing force of the heater constant, it is necessary to press the heater onto the sleeve by use of an elastic member. In the disclosure of Patent Document 8, a heater is pressed onto a sleeve by use of an elastic member and a cam.
More specifically, Patent Document 8 also discloses the constitution in which the cam is disposed between right-and-left arranged heaters, each heater is pressed by the elastic member such as a spring, and the heater is pressed onto a heat shrinkable sleeve by rotating the cam using a motor.
Hereinbelow, while pressing two heaters by spring as described above, a system of driving the heater by the cam inserted therebetween will be described with reference to FIG. 32 (a) to (c).
FIG. 32 (a) shows a state shortly after a sleeve 312 is set between two heaters 321 and 322 and before heating is started.
In the drawing, an optical fiber 311 provided inside the sleeve 312 is located on the center line S indicated by a dashed-dotted line.
Moreover, the position of the optical fiber 311 is held and fixed by clamps which are positioned in front of and at the rear side of the heaters 321 and 322 and not shown in the figure.
Subsequently, as shown in FIG. 32 (b), a cam 323 rotates, the two heaters 321 and 322 are pressed onto the sleeve 312 by forces of compression coil springs 324 and 325, and heating of the heaters 321 and 322 is thereby started.
In the drawing, the cam 323 does not come into contact with movable tables 321A and 322A, and the sleeve 312 is pressed by the forces of the compression coil springs 324 and 325.
At this time, as long as the position of the optical fiber 311 is located on the center line S indicated by a dashed-dotted line, an excessive tension is not applied to the optical fiber 311.
Next, as it is in this state, the sleeve 312 shrinks, thereafter being completely shrunk, and heating reinforcement is completed. In this situation, if the position of the optical fiber 311 does not displace from the center line S as described above, an excessive tension is not applied to the optical fiber 311.
However, as a practical matter, the pressing forces of the right-and-left arranged compression coil springs 324 and 325 in the drawing are not the same as each other, the sleeve 312 does not stay on the center line S, and it is difficult for the two compression coil springs 324 and 325 to be always located at the same position while being continuously balanced for a long period of time.
For example, as shown in FIG. 32 (c), in a general state, the compression coil springs 324 and 325 are located near the side of any one thereof due to a difference in force between the compression coil springs.
In the state shown in FIG. 32 (c), the movable table 321A that is disposed at the left side in the drawing is brought into butt-contact with the left-side housing and stopped.
For this reason, in FIG. 32 (c), the position of the optical fiber 311 is displaced from the center line S; furthermore, since the optical fiber 311 is fixed by the clamp which is not shown in the figure, if the above-mentioned slight displacement occurs, the excessive tensions of the compression coil springs 324 and 325 are applied to the optical fiber 311.
In the technique disclosed in Patent Document 8, there is a second problem in that an excessive pressing force is applied to the optical fiber.
The force of approximately 500 gf by which the sleeve is pressed is extremely larger than the tension of approximately 30 gf which can be applied to the above-described post-fusion-spliced optical fiber, this force is two or more times the tension of 200 gf under the rupture evaluation test, and therefore, there is a concern that the optical fiber is broken at the moment at which the pressing force is applied thereto.
Even if breaking does not occur, the long-term reliability of the optical fiber is degraded.
In the technique disclosed in Patent Document 8, there is a third problem in that a mechanism that applies a tension to the optical fiber is necessary.
In the method of pressing both sides of the sleeve 312 as described above, before performing the pressing by the heaters 321 and 322, it is necessary for the sleeve 312 to be in the state of being suspended from the optical fiber 311 to which a tension is applied in advance.
However, as shown in FIGS. 33 (a) and (b), in a case where the clamps 326 and 327 grasps the optical fiber 311 in a state in which a tension is not applied to the optical fiber, slack of the optical fiber 311 occurs immediately after clamping, and the position of the sleeve 312 is displaced downward.
In the foregoing case, as shown in FIGS. 33 (a) and (b), the sleeve 312 is not pressed at a proper position by the heaters 321 and 322, there is a concern that the work operation therefor is completed in a state in which shrinkage is not completed.
As a countermeasure against this case, it is thought that the heaters 321 and 322 are configured to be longer in the vertical direction thereof in consideration of the case where the position of the sleeve 312 is displaced downward; however, as the heaters 321 and 322 are larger in size, the heat capacity thereof increases, and there is a problem in that the rate of temperature increase decreases.
As a method of removing such slack of the above-mentioned optical fiber, it is required that a fixed tension is applied to a clamp grasping the optical fiber by use of, for example, an elastic member such as a spring or a magnetic member such as a magnet.
That is, in the two method described in the explanation of the above-described Patent Document 4, the method of using a magnetic force described in Patent Document 5, the method of Patent Document 6, it is necessary to apply a tension to the optical fiber.
In the technique disclosed in Patent Document 8, there is a fourth problem due to the size of the device.
By using a micrometer or a screw mechanism as a system of driving the heater, it is possible to provide a pressing force exceeding 500 gf.
However, since a fusion splicer that splices optical fibers is used on above a telegraph pole or in a narrow space such as a narrow manhole and since it is necessary to splice optical fibers having even a shorter excess length, a reduction in device size is required.
Because of this, in the case where two motors and two micrometers or two screw mechanisms are provided inside such fusion splicer, the device size increases, and there is a problem in that it is not suitable to a work operation environment or it is possible to splice optical fibers having a shorter excess length.
As a result, a fusion splicer provided with a drive mechanism obtaining the above-mentioned pressing force is not put to practical use.
Even in the case of using any technique described in the aforementioned Patent Documents 4, 5, and 6 in order to apply a tension to an optical fiber, since the movable clamp cannot move forward to the direction of the heater after the optical fiber is clamped, as a result, the movable clamp cannot absorb this tension when a large tension is applied to the optical fiber by the pressure of the heater.
Accordingly, it is not possible to remove the tension that is excessively applied to the optical fiber, there is a problem causing breaking of the optical fiber or degradation in long-term reliability thereof.
That is, in a conventional reinforcing heating device, due to the problem of the long-term reliability of the optical fiber, the sleeve cannot be pressed so as to be deformed.
By use of the technique described in the above-described Patent Document 8, it is possible to realize that a sleeve is pressed by the force exceeding a tension under a rupture evaluation test; however, a variety of mechanism elements as well as a motor is necessary, as a result, the device becomes larger in size.
That is, in a conventional reinforcing heating device, due to a limitation in device size, the sleeve cannot be pressed so as to be deformed.